Hi, I think that we've got evidence that the reduced evaporative demand coupled with the reduced transpiration from plants more-than-offsets the reduced precip in many regions for sunshade geo + high CO2. P-E is positive in many regions which show reduced precip in the G1 experiment (see Glienke et al. above for some examples and figure 5 in Kravitz et al. 2013) and I'm sure it must be so for strat aerosol geo too, though most studies only describe precipitation changes. The study by Donohue et al. (2013; copied below) found that higher CO2 is resulting in a greening of arid regions, once variations in precipitation are factored out. This means that rising CO2 is in effect shifting what constitutes 'arid' conditions for vegetation as they can use water more efficiently.
http://onlinelibrary.wiley.com/doi/10.1002/grl.50563/full Thus we can't presume that a relative climatological drying of a region under a high-CO2 + SRM scenario when compared against a low-CO2 baseline state will actually give rise to water stress for vegetation as they will be much better able to deal with drier conditions. I think this is reflected in your results and the results of Susanne - vegetation productivity is higher almost everywhere despite reductions in precipitation and precipitation-evaporation in many regions. I think this issue needs further study but my intuition is that the threat posed by reduced precipitation with solar geoengineering is less threatening than presumed to date. We need a more nuanced, impacts-focused view of the hydrological implications of SRM. cheers, Pete Peter J. Irvine Postdoctoral Fellow Harvard University John A. Paulson School of Engineering and Applied Sciences (SEAS) One Brattle Square, Office 492, Cambridge, MA 02138, USA Email: [email protected] <[email protected]> https://scholar.google.de/citations?user=7asLSCEAAAAJ&hl=en On 12 February 2016 at 11:08, Lili Xia <[email protected]> wrote: > Hi, Peter, > > The evaporation reduction due to cooler environment would balance the > effect of the reduced precip to some extent. The change of > evapotranspiration may help. I think more studies are needed to work on all > the details. > > Lili > > On Thu, Feb 11, 2016 at 6:38 PM, Peter Irvine <[email protected]> > wrote: > >> Interesting study Lili! One surprise for me was the large increases in >> productivity in the amazon - do you think that the temperature reduction >> and reduced evaporative demand more than make up for the reduced precip? >> >> I'm looking forward to the next-gen of nitrogen-limited models getting >> into this debate, they produced a different sign of change in Susanne's >> study. Cooler was worse for productivity in the tropics rather than better, >> despite the factors you identify in your study due to the greater >> availability of nitrogen in the warmer soils. This effect is obviously >> missing from models without interactive nitrogen cycles >> >> Pete >> >> Pete >> >> Peter J. Irvine >> >> Postdoctoral Fellow >> Harvard University >> John A. Paulson School of Engineering and Applied Sciences (SEAS) >> One Brattle Square, Office 492, Cambridge, MA 02138, USA >> >> Email: [email protected] <[email protected]> >> https://scholar.google.de/citations?user=7asLSCEAAAAJ&hl=en >> >> On 11 February 2016 at 15:35, Lili Xia <[email protected]> wrote: >> >>> Hi, Peter, >>> >>> I think there are couples things which make the results different: (1) >>> G1 doesn't have diffuse radiation increasing; (2) CLM in Xia et al. is >>> CLM-SP instead of CLM-CN; (3) the climate forcing is quite different. >>> >>> Lili >>> >>> On Thu, Feb 11, 2016 at 12:11 PM, p.j.irvine <[email protected]> >>> wrote: >>> >>>> Hi, >>>> >>>> I wouldn't be so sure that this is a forcing difference. There are VERY >>>> large differences in the model response to high CO2 scenarios, with much >>>> smaller differences between SRM and no-SRM scenarios. These arise because >>>> different factors act to limit vegetation productivity in the different >>>> models. In Susanne Glienke's paper the only models which included a >>>> nitrogen cycle in GeoMIP, a version of CLM, found the opposite trend to >>>> that reported in Xia et al. They found greater tropical productivity in the >>>> non-SRM scenario than the SRM scenario and only a small CO2 fertilization >>>> effect, likely arising from the fact that nitrogen is the limiting factor >>>> in these regions and it is recycled more rapidly in warmer soils boosting >>>> NPP. >>>> >>>> I think it's still early days in the study of the vegetation response >>>> to SRM. >>>> >>>> cheers, >>>> >>>> Pete >>>> >>>> On Thursday, 11 February 2016 08:44:01 UTC-5, Alan Robock wrote: >>>>> >>>>> Dear Bala, >>>>> >>>>> Actually in our paper we say: >>>>> >>>>> Kalidindi et al. (2015) showed that with a 20 Tg sulfate aerosol >>>>> (SO4) stratospheric loading to balance the radiative forcing >>>>> of 2 xCO2, broadband diffuse radiation would increase >>>>> by 11.2 Wm-2 compared with the reference run. However >>>>> they used a very unrealistic stratospheric aerosol distribution, >>>>> with a very small effective radius of 0.17 μm and uniform >>>>> geographical distribution. >>>>> >>>>> So we did different experiments, and we used a much more "realistic" >>>>> aerosol size and space distribution. I think the differences in the >>>>> results are because of the forcing and not the models. >>>>> >>>>> Alan >>>>> >>>>> Alan Robock, Distinguished Professor >>>>> Editor, Reviews of Geophysics >>>>> Department of Environmental Sciences Phone: +1-848-932-5751 >>>>> Rutgers University Fax: +1-732-932-8644 >>>>> 14 College Farm Road E-mail: [email protected] >>>>> New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock >>>>> ☮ http://twitter.com/AlanRobock >>>>> Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54 >>>>> >>>>> On 2/10/2016 10:32 PM, Govindasamy Bala wrote: >>>>> >>>>> Interesting result. The conclusions seem to depend on model >>>>> configurations. >>>>> >>>>> Our paper published last year in Climate Dynamics (attached) did not >>>>> find any such benefit from the enhanced diffused radiation because of the >>>>> offset from a reduction in direct light. In fact we found a net reduction >>>>> in GPP of about 1 PgC >>>>> >>>>> Looks like Multi-model intercomparison would be needed to resolve this >>>>> issue. >>>>> >>>>> On Wed, Feb 10, 2016 at 7:39 PM, Alan Robock < >>>>> [email protected]> wrote: >>>>> >>>>>> Our most recent paper has just been published: >>>>>> >>>>>> Xia, L., Robock, A., Tilmes, S., and Neely III, R. R.: Stratospheric >>>>>> sulfate geoengineering could enhance the terrestrial photosynthesis rate, >>>>>> Atmos. Chem. Phys., 16, 1479-1489, doi:10.5194/acp-16-1479-2016, >>>>>> 2016. >>>>>> >>>>>> http://www.atmos-chem-phys.net/16/1479/2016/ >>>>>> >>>>>> -- >>>>>> Alan Robock >>>>>> >>>>>> Alan Robock, Distinguished Professor >>>>>> Editor, Reviews of Geophysics >>>>>> Department of Environmental Sciences Phone: >>>>>> +1-848-932-5751 >>>>>> Rutgers University Fax: >>>>>> +1-732-932-8644 >>>>>> 14 College Farm Road E-mail: >>>>>> [email protected] >>>>>> New Brunswick, NJ 08901-8551 USA >>>>>> <http://envsci.rutgers.edu/%7Erobock> >>>>>> http://envsci.rutgers.edu/~robock >>>>>> ☮ http://twitter.com/AlanRobock >>>>>> Watch my 18 min TEDx talk at >>>>>> http://www.youtube.com/watch?v=qsrEk1oZ-54 >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "geoengineering" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to [email protected]. >>>>>> To post to this group, send email to [email protected]. >>>>>> Visit this group at https://groups.google.com/group/geoengineering. >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> With Best Wishes, >>>>> >>>>> ------------------------------------------------------------------- >>>>> G. Bala >>>>> Professor >>>>> Center for Atmospheric and Oceanic Sciences >>>>> Indian Institute of Science >>>>> Bangalore - 560 012 >>>>> India >>>>> >>>>> Tel: +91 80 2293 3428; +91 80 2293 2505 >>>>> Fax: +91 80 2360 0865; +91 80 2293 3425 >>>>> Email: [email protected]; [email protected] >>>>> Web:http://caos.iisc.ernet.in/faculty/gbala/gbala.html >>>>> ------------------------------------------------------------------- >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "geoengineering" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To post to this group, send email to [email protected]. >>>>> Visit this group at https://groups.google.com/group/geoengineering. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>>> >>>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "geoengineering" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To post to this group, send email to [email protected]. >>>> Visit this group at https://groups.google.com/group/geoengineering. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> >> > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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